A new absorbent system for reducing chlorine gas escape and enhancing pollutants removal during ship exhaust wet scrubbing

Abstract

Using chlorine-containing oxidants to remove pollutants in the exhaust gas of ships is normally accompanied by Cl2 escape, which poses a significant threat to the environment and the health of the crew. This paper proposes a method to solve the problem of Cl2 escape in a single NaClO solution system using BAD (a new amide absorbent, C12H25NO). The electrostatic potential (ESP) theoretical calculations, FT-IR and UV–vis spectra tests showed that the strong field effect interaction between BAD and Cl2, which can form a stable symmetrical structure similar to a “sandwich”, results in a strong binding ability of BAD to Cl2. The effects of the initial pH, the concentration of NaClO solution, aeration time, and some operating parameters on the loss of active chlorine (AC) components were studied. Under the same conditions, a two-phase composite absorbent system with the addition of BAD can reduce the loss of AC components by 32.67% on average and up to 56.12%. It also can effectively capture the Cl2 escaping with the gas flow and keep it in the system, which enhances the oxidation of NO by Cl2 at the gas–liquid interface. It also has a strong ability to remove pollutants for a long period, as the removal efficiencies of SO2, NO, and NOx within 20 mins were 97.84%, 77.98%, and 76.01%, respectively. The results show that the BAD-NaClO two-phase composite absorbent system can effectively reduce Cl2 escape, and it is a sustainable wet treatment scheme for ship exhaust gas with great application prospects.